Osmotic devices for delivering a beneficial agent including a medicine to an environment of use are known to the prior art in U.S. Pat. No. 3,845,770, issued to Theeuwes and Higuchi, and in U.S. Pat. No. 3,916,899 issued to the same patentees. The osmotic devices disclosed in these patents comprise a compartment containing a beneficial agent including a medicine. The semipermeable wall is permeable to the passage of an external fluid and it is substantially impermeable to the passage of the beneficial agent including medicine. An osmotic passageway is provided through the wall for delivering the beneficial agent from the device. These prior art osmotic devices release the beneficial agent by imbibing fluid through the semipermeable wall into the compartment to form in the device an aqueous solution containing the beneficial agent that is dispensed through the passageway from the device. The external fluid is imbibed through the semipermeable wall into the compartment in a tendency towards osmotic equilibrium at a rate determined by the permeability of the semipermeable wall and the osmotic pressure gradient across the wall. These devices are extraordinarily effective for delivering an agent that is soluble in the fluid and exhibits an osmotic pressure gradient across the semipermeable wall against the external fluid, and for delivering an agent that has limited solubility in the fluid and is admixed with an osmotically effective osmagnet that is soluble in the fluid and exhibits an osmotic pressure gradient across the semipermeable wall against the fluid. The agent is incorporated into these devices during manufacture, prior to forming the semipermeable wall around the compartment. These prior art osmotic devices generally contained a large amount of a beneficial agent, and they operate successfully for delivering the beneficial agent to the environment of use.
The devices commence to deliver the beneficial agent as soon as the external fluid is imbibed through the semipermeable wall to form a solution containing the beneficial agent that is osmotically pumped from the device. The presently available osmotic delivery devices, when used in the fields of medicine and pharmacy for orally delivering a beneficial medicine to the stomach of a gastrointestinal tract, commence to dispense the beneficial medicine as soon as the osmotic device enters the fluid-rich environment of the stomach.